The HO-1/CO system is a significant part of the defense against the damage inflicted by a variety of stress conditions mediated by heavy metals, reactive oxygen species, lipopolysaccharide (LPS) and other inflammatory processes, thereby playing a pivotal role in the regulation of the cytoprotective and anti-inflammatory responses. CO gas administered at low doses (250 ppm) for restricted period of times has been shown to restore many of the beneficial effects of HO-1 in models of cardiovascular dysfunction, pulmonary hypertension, and inflammatory conditions such as sepsis and inflammatory bowel disease.
Because of the interest in HO-1/CO therapeutic potential, compounds that liberate controlled amounts of CO (CO-releasing molecules, CO-RMs) to biological systems have been developed and demonstrated to exert a wide array of pharmacological effects related to CO release. The vast majority of pharmacologically active CO-RMs described in the literature are metal carbonyls containing either Ru, Fe, Mn, Co and Mo.
The transcription factor Nrf2 is a crucial initiator of the cellular stress response as it co-ordinates the expression of several antioxidant and detoxification genes that repair damage and restore cellular homeostasis. As part of this inducible response, heme oxygenase-1 (HO-1) plays a prominent role by utilizing heme to produce CO, biliverdin/bilirubin and iron, important signaling and protective molecules against oxidative stress and inflammation.
The list of Nrf2/HO-1 activators has now grown to include several hundred compounds. Because of their mechanism of action, Nrf2/HO-1 activators require time to mount the cellular stress response, resulting in a delayed, albeit essential, beneficial effect.
WO 2012/076696 discloses curcumin derivatives bound to a CO-releasing molecule. The inventors of the present invention have however shown that these molecules do not release carbon monoxide. This lack of CO-release results in molecules that do not exhibit the wide array of beneficial therapeutic effects related to the activation of HO-1 by CO.
The synthesis and preliminary biological characterization of two fumarate-CORM molecules exhibiting the dual ability to activate the Nrf2/HO-1 cytoprotective pathway and to release controlled amounts of CO have been reported (Wilson et al. Chem. Eur. J. 2014, 20, 14698-14704).
Antioxidant and detoxification genes transcribed after Nrf2 activation include those involved in the synthesis of glutathione, the most important and abundant cellular thiol protecting against oxidative stress. As proposed by Satoh and Lipton (Sato T et al. Free Rad. Biol. Med. 2013, 65, 645-657), drugs developed as Nrf2 activators should be evaluated for their two opposing actions: cytoprotective versus cytotoxic effects. The cytoprotective effects are due to the extent of activation of Nrf2-dependent genes while cytotoxicity involves glutathione (GSH) depletion. Thus, in terms of tolerability, it is desirable to produce compounds that cause a strong Nrf2-dependent response without markedly depleting GSH content, and with a low cytotoxicity.
Hence, there is a need to find enhanced hybrids containing an Nrf2 inducer bound to a CO-releasing molecule, that will provide greater tissue protection by first limiting damage through CO delivery and subsequently promoting the endogenous up-regulation of Nrf2-dependent defensive genes and proteins, a process that takes several hours due to transcription and translation processes.